1. Field of the Invention
The present invention relates to an optical sensor device. More specifically, the present invention relates to a package structure of the optical sensor device.
2. Description of the Related Art
FIG. 11 is a sectional view illustrating an example of a related-art package (FIG. 2 of Japanese Patent Application Laid-open No. 2002-198455). This package has the following structure. A package body 21 includes a lead 25 and a cavity formed by a bottomed portion 23 and an inner side surface 24 that are made of a resin material. A semiconductor element 22 is mounted on the bottomed portion 23 of the package body 21, and a lid 27 is provided on a package upper surface. A surface of a part of the lead 25 is exposed from the bottomed portion 23, and another part of the lead 25 is exposed to outside through the package formed of a resin molded portion so as to be used as an external terminal. An electrode is formed on a surface of the element 22. The electrode formed on the surface of the element 22 and the lead 25 exposed from the bottomed portion 23 of the cavity are electrically connected to each other through a wire 26. For example, in the case of a light-receiving sensor device having a light-receiving element mounted thereon, the light-receiving element receives light from an external light source, including natural light. Alternatively, light from a light-emitting device is radiated to an object and the light-receiving element receives light reflected from the object. Thus, a generated electromotive force can be transmitted from the electrode formed on the surface of the element to outside through the lead 25 via the wire 26.
Further, FIG. 12 is a sectional view illustrating another example of a related-art package (FIG. 1 of Japanese Patent Application Laid-open No. Hei 04-157759). This package has the following structure. An optical semiconductor element 22 and a wire 26 mounted on a die pad 27 and a lead 25 forming a die pad and a lead are sealed with a transparent mold resin 28 formed of an epoxy resin, and a transparent plate member 29 made of glass or plastic is arranged on a surface of the transparent mold resin 28 in a direction immediately above the optical semiconductor element 22. An upper surface of the optical semiconductor element 22 serves as a light-receiving surface 22a, and an electrode formed on the upper surface and a part of the lead 25 sealed with the transparent mold resin 28 are electrically connected to each other through the wire 26. The lead 25 is exposed to outside through the transparent mold resin 28 so as to be used as an external lead. In the case where the optical semiconductor element 22 is used as, for example, a light-receiving sensor device having a light-receiving element mounted thereon, light from outside passes through the transparent plate member 29 and through the transparent mold resin 28 to be received by the light-receiving surface 22a of the optical semiconductor element 22. Thus, a generated electromotive force can be transmitted from the electrode formed on the surface of the element to outside through the lead 25 via the wire 26.
However, in the package structure described in Japanese Patent Application Laid-open No. 2002-198455, the lead 25 is held only with the resin of the package body 21 forming the cavity. Specifically, a portion of the lead 25, excluding a part serving as the external terminal exposed to outside through the resin forming the cavity and a wire bonding portion exposed from the surface of the bottomed portion 23 of the cavity, is held only with the resin so as to be in close contact therewith. In this structure, there are the following problems: the removal preventing force of the lead is low; the holding area thereof is small; and the lead surface made of a metal has low adhesion to the resin. Further, in the case where the part of the lead 25 serving as the external lead terminal is bent and cut, mechanical stress is concentrated on a root portion between the molding resin and the lead 25 exposed to outside from the molding resin, so that the resin is liable to be peeled and cracked. Further, a gap remains at an interface between the lead 25 and the resin, with the result that the package has low airtightness. Therefore, it is difficult to obtain a strong holding force of the lead 25. Further, there is also a problem in that water is liable to enter the package from outside, and in addition, ambient environment may change. Thus, it becomes more difficult to obtain high reliability.
Further, in the package structure described in Japanese Patent Application Laid-open No. Hei 04-157759, the entire peripheries of the optical semiconductor element 22, the wire 26, the die pad 27, and the lead 25 are sealed with the transparent mold resin 28, with the result that the contact area between the lead 25 and the transparent mold resin 28 is increased, and the holding force of the lead 25 can also be increased. However, even in the structure in which the periphery of the lead 25 is sealed with the transparent mold resin 28 formed of an epoxy resin, the adhesion between the metal and the resin is not sufficient, and there is a significant difference in expansion coefficient between the metal and the resin. Thus, it cannot be considered that the adhesion between the die pad 27 and lead 25 and the transparent mold resin 28 is sufficient, and a gap remains therebetween, which degrades airtightness. Further, in the case where the external lead is bent and cut in the structure in which the lead 25 is sealed with the transparent mold resin 28 formed of an epoxy resin, stress is concentrated on the transparent mold resin 28. Therefore, the transparent mold resin 28 is liable to be cracked and chipped, and further, a gap is liable to be formed between the transparent mold resin 28 and the lead 25. In addition, there is a risk in that an external appearance of the package may be impaired. Therefore, there is a demand for means for enhancing the adhesion between the lead and the resin, achieving strong resistance to stress during processing, and increasing the holding force of the lead.